The present invention relates to a device, system and method for stereotactic medical procedures. More specifically, it provides for accurate positioning (fixation) of a patient or part of a patient for carrying out medical procedures, singly or multiple times.
The discussion below will initially focus on medical procedures where the procedure is performed multiple times on the same patient.
Various medical procedures involve repeated treatments at different times. For example, application of radiation is sometimes used for treating cancer or other conditions. Although a single application of radiation may sometimes be used, under many circumstances there are sound medical reasons to use repeated application of radiation at different times.
There are other medical procedures where precise location of patient features are required either for a one time therapeutic treatment or a repeated treatment.
There are situations when the localization procedure and the therapeutic procedure must be carried out at either different times or at different locations, such as a CT scan or MR scan followed by a surgical or radiosurgical procedure.
Radiosurgical technique, among other medical procedures, uses stereotactic principles for targeting, localization and treatment. The procedure begins with a stereotactic reference system being fixed to the patient's skull. This reference system remains fixed relative to all intracranial points throughout the entire radiosurgical procedure. All diagnostic exams, such as angiography, CT and MR scanning include a set of fiducial markers which allow all points within the image to be localized relative to the stereotactic reference frame. All of these fiducial system attach to the stereotactic frame in a precision and reproducible manner.
The present inventors' prior U.S. patents listed below, assigned to the assignee of the present application, and hereby incorporated by reference disclose techniques for providing stereotactic radiosurgery with a high degree of precision: U.S. Pat. No. 5,027,818 issued Jul. 2, 1991, titled DOSIMETRIC TECHNIQUE FOR STEREOTACTIC RADIOSURGERY; and U.S. Pat. No. 5,189,687 issued Feb. 23, 1993 APPARATUS FOR STEREO-TACTIC RADIOSURGERY. The techniques of the inventors' above patents allow the patient to be precisely positioned relative to radiation beams of stereotactic radiosurgery to within 0.2 mm plus or minus 0.1 mm. Although this works very well for single fraction therapy, there exist clinical settings where fractionating the total dose, i.e. dividing the dose into many small fractions, would yield additional therapeutic advantage. In the radiotherapy procedure, once the reference frame has been removed from the patient the relationship between intracranial target points and the reference system is lost. Because the above procedure would require the reference frame to remain fixed to the patient's skull through the entire course of treatment, which may last several weeks, this approach is considered inappropriate for fractionated therapy. Alternately, each fractional treatment would require a laborious and time-consuming procedure to re-determine patient position for second and subsequent treatments.
Another setting would be where the patient undergoes a medical imaging procedure to be followed by stereotactic or optic guided surgery. In this setting the patient is scanned prior, sometimes a day or two before, the surgical procedure. The registration of the patient's scan data set to their position on the operative setting is carried out through the use of surface fiducials. This usually entails the shaving of the patient head.
There exist several different techniques for non-invasive repeat fixation. These methods can be broken down into three basic categories. These are bite plate systems, contour realignment systems and mask systems. All of these systems have design flaws which can lead to unacceptable, and undetectable, positional errors.
The mask techniques have been used in radiation therapy for over three decades. In these systems a custom mask, which snugly fits either the face or the entire head, is fabricated. For high precision radiotherapy the mask is then attached to a stereotactic reference frame, similar to the frame used for any stereotactic procedure. Prior to each diagnostic exam the patient is placed into the mask/frame system and normal stereotactic fiducial systems are used for image registration.
Mask immobilization and repositioning systems have been used extensively in radiation therapy. By using the mask for both localization (i.e., determination of position and orientation) and positioning (i.e., the mask or mechanisms rigidly secured to it are used to move the patient), the positioning puts loads (forces and/or moments) on the mask which may distort it. Distorting the mask introduces errors which hinder accuracy of localization.
When performing fractionated radiotherapy, accuracy in applying the radiation is very important. Some tumors or other conditions require that the radiation be concentrated in relatively small volumes. Misalignment of the radiation beam may cause an insufficient amount of radiation to be applied to the tumor or other target. Further, such misalignment may increase the likelihood and/or degree of damage to healthy tissue adjacent the tumor or other target.
Fractionated radiotherapy may be imprecise if the tumor or other target cannot be localized with a sufficient degree of accuracy. However, this need for proper localization is the same need which one has when performing single dose radiotherapy and this need is addressed by the present inventors' two first listed below incorporated by reference patents. The additional factor in fractionated radiotherapy is the need to easily and accurately repeat a position of the patient. If the position of the patient was accurate relative to the first treatment, and relative to the imaged data set used to design the treatment, the repositioning should normally cause the patient to assume the exact same position (relative to the treatment mechanism) for the second and subsequent treatments. However, if the second or other subsequent treatment is performed with the patient only slightly moved from the first treatment position, this will introduce inaccuracies. The repeat fixation techniques discussed above have the indicated disadvantages.
More generally, the need for repeat fixation of a patient or portion of a patient exists outside of radiotherapy. In the general case, one wishes to perform a first medical procedure on a patient with a precise localization of portions of the patient, and, at some later time, perform a second medical procedure on the patient with a precise localization of portions of the patient. One can repeat laborious and time-consuming localization steps for the second medical procedure, but this increases medical costs and complexity. As used herein, a medical procedure is a procedure for diagnostic and/or remedial purposes.
In some situations, a single medical treatment without a need for repeat fixation is the desired course of treatment. However, a high degree of accuracy in positioning may still be required. The mechanical arrangements and the associated techniques of the present inventors' last mentioned above two above incorporated by reference patents can provide a high degree of accuracy in positioning of the patient relative to the medical apparatus.
The present inventors' prior U.S. patents listed below, assigned to the assignee of the present application, and hereby incorporated by reference disclose techniques for providing determination of patient position with a high degree of precision for stereotactic radiosurgery and other medical procedures: U.S. Pat. No. 5,954,647 issued Sep. 21, 1999, titled MARKER SYSTEM AND RELATED STEREOTACTIC PROCEDURE; and U.S. Pat. No. 5,588,430 issued Feb. 14, 1995 titled REPEAT FIXATION FOR FRAMELESS STEREOTACTIC PROCEDURE. These patents disclose various locators using bite plates, head rings, and/or masks. The bite plates are used for repeat fixation medical procedures (i.e., where procedure is performed with locator on patient, locator and any other associated parts are then removed from the patient, and, at a later time, locator is placed back on patient).
It is now common for medical clinicians to obtain high contrast and high spatial resolution computerized tomography (CT) and magnetic resonance (MR) data sets. These data sets can be obtained with high spatial resolution between contiguous image slices. These data sets allow for the reconstruction of a precise 3-dimensional (3D) model that accurately describes both the patient's external and internal anatomy. The patient specific models can be manipulated to provide reconstructed views along orthogonal or oblique planes through the patient's anatomy. These computed views allow for clinicians to carry out virtual treatments (or virtual planning) to better optimize therapy for a patient.
Virtual planning is used in several different types of therapy. Radiosurgery, stereotactic radiation therapy, and routine radiotherapy are all therapies that rely upon virtual planning to position radiation beams. Image guided surgery relies upon virtual planning to allow the surgeon to design and evaluate various surgical approaches and to target specific tissues. The virtual planning process places a unique requirement on the basic 3D image data set, that being the ability to track the patient, at the time of therapy, relative to the therapeutic tool. For radiosurgery, stereotactic radiation therapy and radiation therapy, the therapeutic tool is the radiation-generating device, most commonly, a medical linear accelerator. In the case of image guided surgery, the therapeutic tool can be one of a number of devices that the surgeon my use. For example, scalpels, biopsy needles, and operating microscopes are a few of the most commonly guided surgical tools.
In order to provide the required patient-tool tracking both the tool's position and the patient's position must be known. The most common method of tracking the patient is to place identifiable reference markers, called fiducial markers, fixed relative to the portion of the patient where treatment is desired. These markers are incorporated into the 3D image data set. They are also available for identification, again on the surface of the patient (fixed relative to the portion of the patient), at the time of the therapeutic procedure. The markers on the patient are registered against their images in the 3D data set. This registration allows the computation of a rigid relationship between the virtual 3D patient and the real patient. Once this registration has been carried out, any movement of the patient can be tracked.
The last two above listed patents of the present inventors disclose, among other systems, methods and devices, a technique using a bite plate as part of a locator. Advantageously, the preferred embodiments of that bite plate are independent of the system used to immobilize (secure in a stable position) and/or move the patient. These bite plates have been quite effective and useful, especially in providing precise position and orientation for the treatment of intracranial tumors. The bite plates were molded to fit the patient's teeth (gums if the patient lacks teeth) and provide a set of fiducial markers located outside the oral cavity. An infrared tracking device views the fiducial markers (also called fiducials) and reports their location relative to the linear accelerator's x-ray beam. The fiducials allow the tracking system to continuously view the reference and thereby provide for real time feedback on the patient's position.
Although the bite plate locator technique has worked quite well for patients with intra-cranial targets, it is not as well suited for other patients. For example, patients that require therapies that significantly irritate the oral cavity can have trouble keeping the bite plate in position. Radiation therapy for head and neck cancer is one of a number of such therapies that often produce severe oral cavity inflammation.